Gallium containing cold-rolled transformer laminations and sheets with a cubic structure

ABSTRACT

Cold-rolled transformer laminations with a cubic structure, containing a maximum of 4 percent by weight of silicon alloyed with 0.0001-0.20 percent by weight of gallium, 0-0.5 percent by weight of nickel and 0-0.5 percent by weight of copper.

United States Patent Stefan et al.

[ 1 Mar. 21, 1972 GALLIUM CONTAINING COLD- ROLLED TRANSFORMERLAMINATIONS AND SHEETS WITH A CUBIC STRUCTURE Mihaly Stefan; FulopBalazs; Zoltan Hegedus; Laszlo Tapolcai, all of Budapest, HungaryInventors:

Assignee: Csepeli Femmu Filed: July 7, 1969 Appl. No.1 839,683

Foreign Application Priority Data References Cited UNITED STATES PATENTS3,008,857 11/1961 Mobius ..148/111 3,239,332 3/1966 Goss ..75/l253,337,373 8/1967 Foster et a1.. ..148/31.55

FOREIGN PATENTS OR APPLICATIONS 651,295 10/1962 Canada ..148/1l0 713,0348/1954 Great Britain ..148/1 1 1 1,372,975 8/1964 France ..148/110Primary Examiner-L. Dewayne Rutledge Assistant ExaminerG. K. WhiteAttorney-Young & Thompson [5 7] ABSTRACT Cold-rolled transformerlaminations with a cubic structure, containing a maximum of 4 percent byweight of silicon alloyed with 0.0001O.2O percent by weight of gallium,0-0.5 percent by weight of nickel and 0-0.5 percent by weight of copper.

4 Claims, No Drawings GALLIUM CONTAINING COLD-ROLLED TRANSFORMERLAMINATIONS AND SHEETS WITH A CUBIC STRUCTURE The invention concernscold-rolled transformer laminations and sheets with a cubic texture. Theinvention further concerns a process for the manufacture thereof.

It is known that the appearancein 1935 of transformer laminations with aso-called Goss texture resulted in great advances in transformerconstruction. Such laminations can be magnetized most easily in thedirection of rolling andtheir magnetic properties are particularly goodin the direction of rolling. Thus e.g., the power loss V of a laminationof thickness 0.35 mm. is not more than 0.48 w./kg., while itsinduction Bin a magnetic field of 25 AW/cm. equals 18,900 G. In the transversedirection, i.e., at right angles to the direction -of rolling, however,the magnetic properties are less advantageous: the power loss V is about1.37 w./kg., whilst-B is only about 12,200 G. Due to the poor magneticproperties in the transverse direction, only those transformers can bemanufactured from transformerlaminations with aGoss texture, whereinthedirection of the magnetic'linesof force coincide with the directionof rolling of the lamination (e.g.,.sectional lamination cores).

It is further known that both in cold-rolled, aswell as in hotrolledtransformer laminations and sheets with isotropic'magnetic properties,the magnetic properties are only slightly different in the rolling andtransverse directions but the optimum magnetic properties which may beachieved with these laminations, are greatly inferior to thecorresponding properties of laminations with a Goss texture: the'powerloss V is 0.8-l .5 w./kg., and the inductionwith a field intensity of 25AW/cm. has a value of 14,500 G.

For exacting electrotechnical applications the magnetic properties ofthe isotropic laminations and sheets are not adequate; such requirementscan only be met by transformer laminations with a cubic structure, whichcan most readily be magnetized in two directions, namelyin the directionof rolling and in the transverse direction in the plane of the sheet.

Transformer laminations with a cubic texture have various advantages,the following being the most important:

a. the magnetic properties are extremely advantageous: the power loss Vis 04-06 w'./kg.- in the longitudinal, as well as in the transversedirection, the initial permeability is 1,500-5 ,000 G/Oe, and themaximum permeability reaches 25,00050,000 G/Oe;

the favorable magnetic properties are approximately equal in thelongitudinal and transverse directions,which makes possible themanufacture of the various E-, U- and M-cores by simple methods;

c. by means of the cold-rolled transformer laminations with a cubictexture, magnetic properties can be achieved, which are equivalent tothose of 45 percent iron-nickel alloys e. g., Permalloy B), whereby,however, the induction is far superior to the values obtainable withthe.iron-- nickel alloys.

For a manufacture of laminations sheets with a cubic texture, the mostimportant, known processes are given in the fol lowing:

a. an alloy containing 20-40 percent of Si or, instead of part of theSi-component, aluminum, and into which also 0.050.3 percent ofmanganeseand a small amount of nickel can be alloyed, is hot-rolled to athickness of about 3.0 mm., then cold-rolled with three to fiveintermediate annealings to 0.04-0.20 mm., and finally thermally treatedfor a longer period (for at" least 24 hours) at 1,200-l,300 C. in a dryhydrogen atmosphere with a dew point below 50 C.;

. as is known, the cubic texture can be improved by arranging nickelalloys or nickel-containing ceramic materials near the surface of thelamination during the last thermal treatment;

. the formation'of the cubic texture can alsobe improved by carrying outthe last two intermediate annealings between l,l and l,300 C.;

d. the cubic texture can advantageously be influenced while respectingcertain requirements in that a small amount of hydrogen sulphide isadded to the gas amount of hydrogen sulphide is added to the gasatmosphere in the course of the final thermal treatment;

as is known, it is possible to manufacture transformer laminations with.a cubic structure starting from a steel ingot crystallizeddirectionally -by suitable methods, after -:an advantageously chosenhot-rolling, subsequent thermal treatment and cold-rolling performedwith intermediate treatment, if during the final thermal treatment a dryhydrogen atmosphere or a vacuum is applied;

. for manufacturing lamination with a cubic texture, afinished,.Goss-textured lamination can be rolled further .intwosteps-with intermediate annealing, after which the final thermaltreatment described under (a) is to be used;

. finally it is known to produce silicon-iron laminations with a cubictexture by means of the original direction of rolling-with respect to 45or 90 rollers in the plane of the sheet.

All these known processes have the common disadvantage that they requirea very strict-observation of the manufacturing technique. Even a smallchange in the rolling system (number of deformations, degree of theindividual deformations) or in the intermediate annealing, or minorchanges in the content of impurities of the alloy, influence theformation of the cubic'texture considerably. The fact that with the sameparticle orientation, different magnetic properties can occur is afurther disadvantage of the known processes. Precisely for these reasonsit is very difficult to manufacture transformer laminations with a cubicstructure on an industrial scale.

.It is the object of the-invention to avoid the grave disadvantages oftheknown methods and to provide a process by means of which transformerlaminations can be mass produced in a simple manner and at low cost.

The invention is based on the following findings:

1. If a certainamount of gallium is added to the steel containing atmost 4 percent by weight of Si, the magnetic properties of theiron-silicon alloys vary most advantageously, the cubic textureformation is considerably increased, the material becoming, however,less sensitive to variations in the rolling and thermal treatmenttechniques.

Of the numerous advantageous effects of alloying with gallium, thefollowing may be mentioned:

' a.- the temperature of the primary recrystallization is varied;

.b. the number of particles in the cubic texture position, formed duringthe primary recrystallization is increased so that the secondaryrecrystallization can consequently be carried out at lower temperatures,whereby the particle size becomes more uniform. All this has an advantageous effect on the magnetic properties, and the quantity of cubictexture-oriented particles reaches 80-90 percent;

. due to the presence of the gallium traces dissolved in the metal, thecrystal surface and crystal boundary energies are considerably variedduring the final thermal treatment, i.e., these values are influencedfavorably relative to the cubic texture formation;

. due to the change in duration of the final thermal treatment and, ifdesired, the use of the magnetic field during cooling, theadjustment ofthe ratios of the initial and maximum permeabilities of the laminationswith a cubic structure is made possible within wide limits.

2. The action of the gallium alloy can be improved by adding certainquantities of one or more further metals (e.g., nickel or copper).

Both findings are surprising since hitherto it hasbeen assumed that forthe manufacture of transformer laminations with a cubic structure it ispreferable to keep the content of impurities and alloying materials ofthe iron-silicon alloys as low as possible and the presence of allalloying constituents,

3. In the case of gallium or of an alloy of gallium with further metals,the best way of avoiding sticking together of the windings and theoxidation or soiling of the lamination surface during the final thermaltreatment is to interpose or insert a wire or strip, consisting of aniron alloy containing 0.5-6 percent by weight of aluminum.

The cold-rolled transformer laminations with a cubic texture accordingto the invention contain a maximum of 4 percent by weight of silicon,alloyed with 0.000l-0.20 percent by weight, preferably 0.04-0.06 percentby weight of gallium, 0.0.5 percent by weight, preferably 0.2-0.4percent by weight of nickel, 0.5 percent by weight, preferably 02-03percent by weight of copper.

The invention further concerns a method for the manufacture of suchcold-rolled transformer laminations and sheets with a cubic texture, bymicro-alloying the iron-silicon base material by successive thermalshaping, descaling, coldrolling, intermediate annealing, final rollingand final thermal treatment of the ingot obtained. According to theinvention one proceeds in such a manner that the micro-alloying of thesteel containing at most 4 percent by weight of silicon is effected with0.000l0.20 percent by weight, preferably 0.04-0.06 percent by weight ofgallium, 00.5 percent by weight, preferably 02-04 percent by weight ofnickel and 0-0.5 percent by weight, preferably 02-03 percent by weightof copper and, if desired, prior to the final thermal treatment, duringthe winding up of laminations a wire or strip consisting of an ironalloy containing 0.5-6.0 percent by weight of aluminum is used as aseparating means between the lamination windings or core parts.

Of the principal advantages of the process according to the invention,the following may be mentioned hereinbelow:

a. as against the known processes for the manufacture of laminationswith a cubic structure, the process according to the invention is moresimple and may be carried out with higher technological tolerances;

b. the initial and maximum permeabilities, coercive force and induction,as well as the power loss of the lamination with a cubic texture can beconsiderably improved;

0. about 80-90 percent of the particles are in the cubic textureposition in the end product;

d. laminations as well as finished cores and parts can be subjected tothe final thermal treatment;

e. the process can be carried out by using known apparatus for themanufacture of transformer laminations with a Goss texture.

Several examples for carrying out the process according to the inventionare given in the following. Example l An iron-silicon alloy with anominal content of 3.2 percent of silicon, 0.05 percent of gallium and0.35 percent of nickel with a very small content of impurities, isproduced in an induction vacuum furnace from a pure iron charge of goodquality, from metallic silicon with a silicon content exceeding 98.5percent and with an aluminum content of less than 0.5 percent, as wellas from metallic nickel. The impurities of the alloy do not exceed thefollowing values: 0.05 percent of carbon, 0.015 percent of sulphur, 0.03percent of chromium, 0.03 percent of molybdenum, 0.93 percent ofvanadium, 0.03 percent of tungsten, 0.01 percent of titanium and 0.005percent of oxygen.

The ingot is hot-rolled to a thickness of 3 mm. at a startingtemperature of l,l00-l,l50 C. The temperature of the lamination is keptabove 900 C. before the last pass.

The scale is removed from the hot-rolled lamination by means of apickling agent containing sulphuric acid and the lamination is thenannealed for 2 hours at 800 C. in a humid hydrogen atmosphere with a dewpoint of +20 C. The lamination is then cold-rolled in several passes toa thickness of 0.80 mm. and, after degreasing, thermally treated for 2hours at a temperature of 850 C. in a hydrogen atmosphere with a dewpoint of 30 C. The lamination is then cold-rolled in several passes to athickness of 0.30 mm. and, after degreasing, thermally treated for 2hours at a temperature of l,000 C. in a vacuum of 10 Torr.

The lamination, the surface of which is metallically pure, iscold-rolled with polished rollers in several passes to a thickness of 0.10 mm. A ribbed strip made of steel containing 1.5 percent of aluminumhaving a clean surface, is inserted between the windings of thedegreased lamination. The thus prepared lamination coil is subjected toa thermal treatment in a vacuum furnace in a vacuum of 10 Torr in such away that during heating the material is kept hot for 2 hours between 550and 700 C.; the temperature is then raised to l,l00 C. and kept for 20hours at this value. After completing the thermal treatment, the chargetogether with the furnace is cooled to 500 C. percent of the particlesof the lamination thus produced are in the cubic texture position; theinitial permeability of the lamination is 4,200 G/Oe and the maximumpermeability 45,000 G/Oe.

Example 2 A lamination cold-rolled according to Example 1 to 3 mm. andproduced from a steel ingot, the composition of which corresponds tothat of Example 1, is descaled in a pickling agent containing sulphuricacid and then subjected for 2 hours to thermal treatment at 800 C. in ahumid hydrogen atmosphere with a dew point of 20 C. The lamination isthen cold-rolled to L0 mm. in several passes and, after degreasing,thermally treated for 2 hours at a temperature of 850 C. in a hydrogenatmosphere with a dew point of30 C. The lamination is then cold-rolledin several passes to a thickness of 0.45 mm. and then-afterdegreasing-subjected for 2 hours to thermal treatment at a temperatureof 1,000 C. in a vacuum of 10' Torr.

The lamination, the surface of which is metallically pure, is finallycold-rolled with polished rollers in several passes to a thickness of0.20 mm. Thereafter one proceeds as in Example 1.

The initial permeability of the lamination thus produced is 4,100 G/Oeand the maximum permeability 37,000 G/Oe. Example 3 One proceeds asdescribed in Example 1 but the silicon content ofthe alloy is adjustedto 2.6 percent by weight, the nickel content to 0.3 percent by weightand the gallium content to 0.05 percent by weight.

The initial permeability of the lamination thus obtained is 4,000 G/Oeand the maximum permeability 38,000 G/Oe. Example 4 One proceeds asdescribed in Example 1 but the final thermal treatment is carried outfor 5 hours.

The initial permeability p of the lamination thus obtained is 3,300 G/Oeand the maximum permeability 24,500 G/Oe. Example 5 One proceeds asdescribed in Example I but the final thermal treatment is carried out ina dry hydrogen atmosphere (dew point below 50 C.) at l,200 C. in such away that this temperature is maintained for 20 hours. In this manner alamination is obtained, the initial permeability of which is 3,700 G/Oeand the maximum permeability 37,000 G/Oe. Example 6 One proceeds asdescribed in Example 1 except that prior to the final thermal treatmentthe desired core sheets are cut out from the lamination, and the thermaltreatment is carried out in such a way that during cooling and onreaching 700 C. the core sheets are exposed to the action of themagnetic field of a field intensity of 10-20 Oe. The initialpermeability i of the maximum permeability 63,000 G/Oe.

We claim:

1. Cold-rolled transformer lamination with a cubic structure, consistingessentially of up to 4 percent by weight of silicon, 0.00l0.20 percentby weight of gallium, 00.5 percent by weight of nickel and 0-0.5 percentby weight of copper, balance essentially iron.

2. Cold-rolled transformer lamination as claimed in claim 1, in whichsaid gallium is 0.040.06 percent by weight, said nickel is 02-04 percentby weight and said copper is 02-03 percent by weight.

3. Cold-rolled transformer lamination as claimed in claim 1, in whichsaid silicon is about 3.2 percent by weight, said gallium is about 005percent by weight and said nickel is about 0.35 percent by weight.

4. Cold-rolled transformer lamination as claimed in claim 1, 5 in whichsaid silicon is about 2.6 percent by weight, said nickel is about 0.3percent by weight and said gallium is about 0.05 percent by weight.

2. Cold-rolled transformer lamination as claimed in claim 1, in whichsaid gallium is 0.04-0.06 percent by weight, said nickel is 0.2-0.4percent by weight and said copper is 0.2-0.3 percent by weight. 3.Cold-rolled transformer lamination as claimed in claim 1, in which saidsilicon is about 3.2 percent by weight, said gallium is about 0.05percent by weight and said nickel is about 0.35 percent by weight. 4.Cold-rolled transformer lamination as claimed in claim 1, in which saidsilicon is about 2.6 percent by weight, said nickel is about 0.3 percentby weight and said gallium is about 0.05 percent by weight.